Field of the Invention
The invention lies in the telecommunications field. More specifically, the invention relates to a method and a home base station for setting up connections for a mobile station in a mobile radio network, whereby the setting up of the connection can be initiated by the home base station or by the mobile station.
Radio communications systems are formed, for example, by mobile radio systems, wireless telephony systems or by radio stations for wireless subscriber connection (RITL radio in the local loop). Mobile radio networks allow communications connections to be set up to mobile subscribers, wireless telephony systems connect specific mobile terminals in the home area, while radio stations for wireless subscriber connection set up communications connections to stationary subscribers. A radio station on the network side is called a base station.
Communications connections are set up and maintained by signaling and wanted information being transmitted via a radio interface. If a plurality of subscribers using the same carrier frequency in the radio interface are separated by different time slots, this is a time-division multiplex system. The time-division multiplex method is referred to as the TDMA (time division multiple access) method. If subscriber signals for different connections are transmitted simultaneously but in different frequency bands, then this is a frequency-division multiplex system (FDMA=frequency division multiple access).
One known mobile radio system is, for example, the GSM (Global System for Mobile Communications) mobile radio network. In addition to time-division multiplex and frequency-division multiplex, other methods may also be used to separate the subscribers at the radio interface. Alternatively or additionally to the the methods for subscriber separation, specific codes may also be used for each communications connection.
A base station is a remote unit, which is normally connected on the network side by wires to other network components, and which is connected via the radio interface to the terminal or some other radio station.
International PCT publication WO 95/02927 discloses a method in which SIM cards (SIM=subscriber identification module) are used to store not only the subscriber number, telephone number and authentication code, but also settings of transmitting/receiving devices in a mobile station and in a home base station. The home base station is thereby connected to a wire-based communications network.
A wireless communications connection can be set up between the mobile station and the home base station by setting the frequency band and transmission power, without any major interference of the surrounding mobile radio network. The tuning to a specific frequency band and the synchronization are, however, related only to the stored settings. The flexibility and accuracy of the communications connection between a mobile station and a home base station is thus limited.
British patent application GB 2 285 556 A and international PCT publication WO 97/11567 disclose radio communications systems with base stations that can be connected to the fixed network for setting up connections to mobile stations. Dedicated synchronization methods are used for that purpose between the base stations and the mobile stations.
A further possibility for parallel use of home base stations and base stations in a mobile radio network is so-called dual-mode terminals, which are designed to set up connections to home base stations via a wireless connection in accordance with the DECT standard (DECT=digital enhanced cordless telephony) and, in addition, for setting up connections to base stations in the mobile radio network in accordance with the GSM Standard. Mutual interference between the various radio interfaces is low, since different frequency bands are used. However, the preparation of radio transmission and signal processing in accordance with both standards involves increased complexity in the mobile stations, leading to less economic solutions.